because I have my completed tasks always hidden unless I specifically search for them, my tasks remain with their status, mostly due to needing to know which were completed by me "Next Actions", were completed by someone else "Waiting For" or "Delegated" or simply a "Reference" that served for something (reference that have no use are simply deleted).

I think it all boils down to what do you use your completed tasks for.

I use Ultimate To Do on Android and completed tasks don't belhave as completed tasts(eg it still shows up where it shouldn't in searches etc. Completed tasks should ONLY show up in the 'Completed tasks' section), so i just delete tasks as soon as they're completed

Otherwise, i think the most logical way is to assign it no status, as ahas been mentioned above.

The checkbox and the "completed" status are redundant. We provide both options so that people can choose how they want to use it. We may add an option to automatically set the status to "completed" when you check off a task.

No, checked off tasks just get marked as checked off. The status doesnt change.

I guess its no big deal overall. Sometimes I look at a completed (checked off) task, and it has a status of something odd, like "waiting" or "planning" because I completed it without changing the status.

Since everything checked off no longer needs an action, auto-changing its status would make sense.